The invention relates to pressure compensated hydraulic valves, wherein a fixed differential pressure is maintained, to maintain a uniform flow rate.
In a hydraulic valve having a reciprocal spool for communicating hydraulic fluid to work ports, it is known to create a fixed differential pressure across the spool by controlling the pressure before the flow has passed through the spool. For example in Wilke U.S. Pat. No. 3,881,512, the hydraulic fluid is preconditioned before it flows across control spool 13 by an initial pressure compensating valve mechanism 15 which divides flow from inlet 18 to either feeder 20 or bypass 19 to keep the flow through work port 22 constant for any given position of spool 13 regardless of fluxuations in pump or load pressure.
In the present invention, a fixed differential pressure is created by controlling pressure after hydraulic flow has passed through the spool.
The present invention evolved from cost reduction efforts to minimize the number and complexity of parts, particularly those requiring machining. This is accomplished in part by marrying certain open flow circuit structure with pressure compensated circuit structure. In an open flow circuit, the flow rate changes in response to load pressure. Unitary open flow hydraulic valves are known having check valves in the same housing as the control spool, typically in the area of a bridge passage between work ports through the spool.
The present invention provides a unitary pressure compensated hydraulic valve, eliminating a separate discreet pressure compensating module. The pressure compensating means of the invention is in the same housing as the control spool. Furthermore, the invention enables known check valve structure and location from open flow circuitry to be applied and used in pressure compensating and shuttle circuits. This facilitates economy of manufacture by enabling use of existing manufacturing steps and assembly line sequences for as much of the valve as possible. The use of check valve structure for pressure compensating and shuttle circuits is further desirable because it typically involves a less expensive stamping operation, as opposed to machining or the like.